This invention relates generally to sensors for sensing physiological functions in a human being and, more particularly, to a clip for positioning and holding an optical sensor adjacent a finger or other body extremity.
Various non-invasive techniques have been developed for sensing physiological functions in a human medical patient. Such non-invasive techniques have the advantage of avoiding physical penetration of the skin. This substantially reduces the risks of infection, trauma and electrical shock and minimizes patient discomfort.
One well known technique for non-invasively sensing physiological functions involves passing infrared or visible light through a portion of a patient's body. By measuring the relative absorption at various wavelengths, information regarding the patient's physiological functions can be derived. Such "optical sensing" is particularly useful in pulse oximetry wherein the instantaneous relative oxygenation of a patient's arterial blood is determined by passing light through a blood-perfused portion of the patient's body (e.g., the finger) and instantaneously measuring the relative absorption at one or more selected wavelengths. Typically, one or more light sources (e.g., light emitting diodes or "LED's") are positioned on one side of the finger, and one or more optical detectors (e.g., photodiodes) are located on the opposite side. A clip device holds both the sources and detectors in their respective, proper positions.
Because it is sometimes necessary to monitor a physiological function for hours, days or even weeks at a time, much consideration must be given to the means by which optical sensing devices are attached or coupled to the patient. On the one hand, a firm means of attachment is desirable in order to ensure continual and reliable monitoring. On the other hand, a too firm means of attachment can cause considerable discomfort, particularly if long term monitoring is involved. Consideration, therefore, must be given to reliability and performance consistent with patient comfort.
Still further consideration should be given to the avoidance of infection and disease transfer. Although non-invasive monitors do not, as a rule, physically enter a patient's body or bloodstream, cleanliness is nevertheless recognized as essential in preventing the spread of disease. Although single-use, disposable devices are one well known way of ensuring sterility and avoiding disease transfer, the disposal of medical waste material is a growing problem, and the costs and waste associated with discarding complex, sophisticated devices after only a single use are becoming increasingly difficult to justify. Preferred devices are those that can be economically manufactured and easily cleaned for multiple use.
One known clip for mounting an optical sensor on a patient's finger is shown in U.S. Pat. No. 4,685,464. In such a clip, a pair of deformable pads, on which are mounted, respectively, a light source and a light detector, in turn are mounted on and adhered to the opposed faces of a rigid, hinged, clothespin-like housing. Although effective, the permanently affixed pads make effective cleaning somewhat difficult and inefficient.